The isotropic particle gun in DDG4 results in a distribution uniform in theta, while a truly isotropic distribution should be uniform in cos(theta). Flat-in-theta gives a too-large number of events in the forward region. If one is an FCAL expert, the current definition is of course favourable, but for more general studies, a truly isotropic distribution would be more convenient!

(This same behaviour was also present in the Mokka particle gun.)

Would it be possible to change the definition of isotropic (in DD4hep/DDG4/src/Geant4IsotropeGenerator.cpp ), or to add the option of using the "correct" definition?